The present invention is directed to fluid compressors suitable for use with vapor-compression cycles and, more particularly, to shaft couplings for orbiting scroll compressors.
Orbiting scroll compressors utilize opposing scrolls to compress a working fluid between two disks along a spirally wound compression path. A stationary scroll includes a first disk having a first spiral wound flange facing an orbiting scroll. The orbiting scroll includes a second disk having a second spiral wound flange that intermeshes with the first spiral wound flange. The first and second spiral wound flanges are disposed between the first and second disks to form a spiral shaped flow path. The second scroll is offset from the first scroll such that the second flange contacts the first flange at intervals of approximately every half-winding of the flow path. As such, the orbiting scroll orbits around the center point of the stationary scroll such that fluid trapped between contact points of the flanges is compressed as it works its way from between the outer windings to between the inner windings as the radius of the windings and the volume of the flow path decrease.
In order to provide the orbiting action of the orbiting scroll, the second disk is connected to a drive shaft through a bearing shaft. The bearing shaft is connected to the drive shaft through a bearing socket having a central axis offset from a central axis of the drive shaft. As the drive shaft rotates about its central axis, the central axis of the bearing socket rotates about, or orbits, the central axis of the drive shaft. As the second flange of the orbiting scroll engages the first flange of the stationary scroll to compress the fluid along the flow path, rotation of the orbiting scroll about the central axis of the bearing shaft is prevented and the bearing socket rotates around the bearing shaft. Thus, the bearing socket and bearing shaft are subject to three-dimensional torque from the mechanical coupling of the drive shaft and the scroll, as well as from the pressure of the compressed fluid flowing through the flanges.
Due the different performance requirements of the scroll and the bearing shaft, it has been typical practice to fabricate the scroll and the bearing shaft from different materials. For example, scrolls are typically comprised of a relatively soft, lubricious material suitable for allowing contact between the flanges. Conversely, bearing shafts are typically comprised of relatively hard, wear-resistant materials suitable for engagement with bearings. It is generally cost-prohibitive to fabricate the scroll from bearing material and performance-prohibitive to fabricate the bearing shaft from scroll material. It therefore becomes necessary to join these components through a coupling that permits each component to function properly and that can withstand the forces transmitted during the compression process. Previous coupling designs have relied on the strength of a single, small diameter threaded fastener that extends through the bearing shaft and the orbiting scroll. The small diameter bolts of these designs are susceptible to breaking and produce stress concentrations within the orbiting scroll, thus limiting the operating speed and power of the compressor. As such, there is a need for a shaft coupling for use in an orbiting scroll compressor that provides suitable material performance and torque transmitting characteristics.